Sapogenin derivatives and preparation of same



Patented Feb. 19, 1946 SAPOGEN IN DERIVATIVES AND PREPARATION OF SAME Russell Earl Marker, Mexico City,

Harry Means Crooks, Jr.,

Wittle, Detroit,

Mexico, and and Eugene Leroy Mich., assignors to Parke, Davis & Company, Detroit, Mich., a corporation of Michigan No Drawing. Original ap Serial No. 393,666. Di

May 24, 1944, Serial 4 Claims.

The invention relates to the preparation of steroidal compounds from glycosidic derivatives of sapogenins. This application is a division of our copending application, Serial No. 393,666, filed May 15, 1941, now Patent No. 2,352,851, issued July 4, 1944.

In the copending application, Serial No. 393,667, filed May 15, 1941, of Russell Earl Marker, now Patent No. 2,352,852, issued July 4, 1944, it is shown that steroidal sapogenins may be isomerized, for example, by treatment with acetic anhydride for six to fifteen hours at about 200 C., to form a new class of sapogenin derivatives designated as pseudo-sapogenins.

In our copending application, Serial No. 537,199, filed May 24, 1944, which is also a division of application, Serial No. 393,666, we have shown and claimed a process by which the pseudo-sapogenins or their ring A and/or B glycosidic derivatives are prepared by reacting glycosidic derivatives of the sapogenins with acidic agents, for example, acylating agents such as acid anhydrides, under conditions more vigorous than those required merely for acylation.

In our parent application, Serial No. 393,666, we have claimed'a process for oxidizing a glycosidic derivative of a pseudo-sapogenin acylated at least at the exo-hydroxyl group and in the sugar residues and hydrolyzing the resulting product with an acidic reagent.

This application relates more specifically to the oxidation of a glycosidic derivative of an exodihydro-pseudo-sapogenin acylated at least at the exo-hydroxyl group and in the sugar residues and the subsequent hydrolysis of. the resulting product.

By glycosidic derivatives of the sapogenins we mean sapogenin derivatives in which sugar residues are attached through a hemi-acetal linkage to the cyclopentanoperhydrophenanthrene plication May 15, 1941, vided and this application No. 537.197

nucleus. In general, the exact nature of the structures of these substances are not known with certainty. The following formulae illustrate various types of the above sapogenin glycosides:

CH; CHI

$11011 (EHOH non VIII. Sarsasapouin CH3 CH3 Generally speaking, the glycosides oi the steroidal sapogenins may be classified as (l) saponins; (2) simpler glycosides. The former usually contains from three to six sugar units, all of which may be the same, or they may be different. The most commonly-occurring sugar units are those of glucose, galactose, rhamnose, and xylose. The simpler glycosides difler from the saponins in that (1) they contain fewer, i. e., one to three, sugar units; (2) they are more readily obtained crystalline; (3) they do not show marked capillary active properties. In most cases, including the compounds represented by VIII, IX, and X, the exact nature of the glycosidic linkages is not definitely known; that is, it is not known whether the sugars have a furanose or pyranose structure, nor which carbon atoms of the difierent sugar units are (through oxygen) united. In many cases even the number and kind of sugar units present are not known.

See further, Fieser, Chemistry of Natural Products Related to Phenanthrene, 2nd ed., p. 333 ff. (Reinhold Publishing Corporation, New York city, 1937.)

Since the steroidal sapogenins occur in nature, not in the free form, but combined with sugar units as glycosidic derivatives, the present invention makes it unnecessary to isolate the sapogenins. Instead, their more readily available glycosides may be converted directly to pseudosapogenin derivatives. This elimination of a formerly essential step results in higher yields of steroidal hormones from plant sources.

In accordance with the invention of this divisional application, a glycosidic derivative of a pseudo-sapogenin acylated at least at the exohydroxyl group and in the sugar residues is first This product may then be hydrolyzed with production of a steroid having in ring D the structure CHI CH:

The above hydrolysis acts both upon the o-acyloxyisocaprooxy group attached to 0-16 and the acylated sugar residues in the other portions of the steroid nucleus. Certain rules can be set down with regard to the products formed during this hydrolysis. The b-acyloxyisocaprooxy group at C-16 is hydrolytically removed with production of a steroid having in ring D the structure CH! CH: 6 0

under conditions of very mild hydrolysis, as for example by treatment with dilute acidic or alkaline reagents. For instance, this group is removed by warming the steroid with dilute alcoholic hydrochloric acid, dilute sodium carbonate solution or dilute barium hydroxide solution. On

the other hand, the acylated sugar residues in catalytically hydrogenated in the side chain'attached to ring D, with production of a glycosidic derivative of an exo-dihydro-pseudo-sapogenin acylated at least at the exo-hydroxyl group and in the sugar residue. This catalytic hydrogenation is accomplished by shaking the glycosidic the remainder of the molecule are affected differently, depending on whether the conditions of hydrolysis are alkaline or acidic. Mild alkaline hydrolysis removes only the acyl groups attached to the sugar residue, while leaving the sugar residues still attached to the steroid nucleus. However, acid hydrolysis removes the sugar residues as well, thereby leaving hydroxyl groups in the steroid nucleus at the position to which the sugar residues were formerly attached. Suitable alkaline reagents for removal of the acyl groups from the sugar residues, while leaving the unacylated sugar residues thus formed still attached to the steroid nucleus, include cold sodium methylate solution, barium hydroxide solution, calcium hydroxide solution and cold sodium hydroxide solution. The acidic hydrolysis required to remove the sugar residues from the steroid nucleus is best achieved by boiling the sults are obtained if the pseudo-sapogenin deriv..

atives are oxidized below 50 C. by means of an oxidizing agent of the class consisting of chromic and permanganic acids and their salts. However, other oxidizing agents such as ozone, hydrogen peroxide, and the like may eiiectively be em played in this step. Particularly satisfactory results are obtained when the oxidation is conducted at 20-35 C. in acetic acid, using chromic anhydride as the oxidant.

It is believed h t h P perties of pseud sapogenins are best explained if the side chain attached to ring D of the cyclopentanoperhydrophenanthrene nucleus be represented by one of the following partial formulae:

on, oom

III

Of these formulae, V seems to account best for the transformations describedin the present invention.

It will be observed that the partial formulae, I,

III, IV, and V all contain a. reactive hydroxyl roup. This hydroxyl group may be acylated to yield compounds which may then be designated as exo-acylates.

In the case of both the terms exo-acylate and exo-dihydro-pseudo-sapogenin, the prefix exo' has the same significance that it does in other branches of organic chemistry, namely, that the particular function involved is exterior to a ring system and in a position not certainty.

The following are specific examples of our invention.

Example 1 The acetate of Trillium erectum pseudo-saponin is obtained as disclosed in application, Serial No. 393,666. It is then catalytically hydrogenated by shaking in an atmosphere of hydrogen in the presence of a catalyst such as platiknown with greater num or Raney nickel while in acetic acid solution. The exo-dihydro-pseudo-trillin acetate thus obtained is dissolved in 2 liters of glacial acetic acid and added at 30 C. to a stirred solution of 25 g. of chromic anhydride'in 1 liter of 60% acetic acid. After the mixture has stood one and a half hours at this temperature, the excess chromic anhydride is destroyed by addition of zinc powder. The solution is filtered from excess zinc and the filtrate is concentrated in vacuo. The residue is dissolved in ether and washed with water and saturated sodium bicarbonate solution. The ethereal solution is evaporated to leave a clear yellow gummy residue weighing about 120 g. This residue consists essentially of the substance representable by the formula,

CH] CH: CH:

The above residue is dissolved in 1% liters of alcohol and a solution of 350 g. of potassium hydroxide in an equal amount of water is added. The solution is refluxed twenty minutes during which time a gum precipitates on the sides of the flask. Then water is added to bring the alcohol concentration down to about 60%. Then enough concentrated hydrochloric acid is added to neutralize the potassium hydroxide (litmus paper test) and to give, an excess of about 50 cc. of concentrated hydrochloric acid. The resulting solution is boiled three hours to complete the hydrolysis.

The solution is now thoroughly extracted with ether and the ethereal layer washed free of alcohol and acid by repeated washing with water and 5% sodium hydroxide solution. Then the ethereal solution is concentrated to leave about 15 g. of an oily residue which is impure A -pregnadienol-3-(p) -one-20. It is best purified by isolating it as the acetate. To do this, the oily residue is acetylated by boiling with 2 volumes of acetic anhydride for about half an hour. Then the acetic anhydride is evaporated under reduced pressure and the residue is crystallized from methanol to yield 7-10 g. of A -pregnadien0l- 3-(p)-one-20 acetate of melting point 174-6 C.

Ez'dmple 2 Pseudo-trillin acetate is obtained from diosgenin as disclosed in application, Serial No. 393,- 666. It is then catalytically hydrogenated as in Example 1 or in the preceding explanation to produce exo-dihydro-pseudo-trillin acetate. To a solution of 4 g. of this product in 200 cc. of acetic acid cooled to 15 C. is added with stirring a solution of 1.2 g. of chromic anhydride in 20 cc. of 90% acetic acid. After the solution has stood for an hour at 25 C. water is added and the product is extracted with ether. The ethereal layer is washed well with water and 5% sodium hydroxide solution. Then the ether is evaporated to leave a crystalline residue. This is refluxed for ninety minutes with 50 cc. of alcohol containing 5 cc. of concentrated hydrochloric acid. Then the mixture is diluted with water, extracted with ether, the ethereal layer washed with water andsodium carbonate solution and then the ether removed on a steam bath. The residue is purified by treatment in the known manner with Girards reagent and the ketone thus obtained distilled in a high vacuum at 120- 140 C. The distillate is crystallized from ether, acetone, and dilute methanol and thus gives A'"-pregnadieno1-3(p)-0ne-20 or melting point 2l0-212 C. Example 3 Pseudo-sarsasapogenin-a-glucoside penta-acetate is obtained from sarsasapogenin as disclosed in application, Serial No. 393,666. This substance may be represented by the following structural formula,

sapogenin. The epi-sarsasapogenin may then be treated to form the glycoside as for example by treatment with bromoacetoglucose.

The conversion of the glycosidic derivative'oi 5. the steroidal sapogenin into an acylated glycosidic pseudo-sapogenin may be eflected by treating the former with an acylating agent under conditions more vigorous than those required for mere acylation. This step may be effected, for example, by treatment of the glycosidic derivatives of the sapogenins with a carboxylic anhydride at 1'75-250 C. We have'found that best results are obtained with lower fatty acid anhydrides while maintaining the reaction temperature in the neighborhood of 200 C. The product thus formed is an acylated glycosidic pseudo sapogenin derivative acylated at least at the exohydroxyl group and in the sugar residues.

It is catalytically hydrogenated to form exo-dihydro-pseudo-sarsasapogenin-a-glucoside pentaacetate and hydrolyzed as in Examples 1 and 2.

The above examples are intended to illustrate but not to limit the present invention and numerous variations in regard to starting materials, conditions of reaction, modes of isolation of the product and other details will be apparent to those skilled in the art after a perusal of this specification.

For example, as naturally occurring glycosidic derivatives of steroidal sapogenins which may be used in the practice of this invention there may be mentioned amolonin, sarsasaponin, digitonin, or like steroidal saponins. Also, there may be used partially degraded glycosidic derivatives of these saponins, such as trillarin or trillin. Such partially degraded glycosidic derivatives of saponins are obtained by hydrolyzing the saponin at some of the oligosaccharide linkages by means of enzymes or dilute acids or similar reagents. Again, there may be used synthetic glycosidic derivatives of steroidal sapogenins such as the synthetic galactosides, glucosides, ribosides, and other glycosides of sapogenins such as sarsasapogenin, diosgenin, or other steroidal sapogenins containing reactive nuclear hydroxyl groups. synthetic glycosides suitable for the practice of this invention may also be prepared from sapogenins which have reactive nuclear hydroxyl groups, but which are not aglycones of naturally occurring saponins. For example, although neither epi-sarsasapogenins nor its glycosides occur in nature, glycosides of epi-sarsasapogenin may be prepared synthetically from sarsasaponin by converting the latter into its aglycone, sarsasapogenin, and then converting this into epi-sarsa- What we claim as our invention is:

1. The process for the preparation of a glycosidic derivative of an exo-dihydro-pseudo-sapog'- enin acylated at least at the exo-hydroxyl group and in the sugar residues which comprises catalytically hydrogenating a glycosidic derivative of a pseudo-sapogenin acylated at least at the exoa hydroxyl group and in the sugar residues.

2. The process for preparing steroidal compounds which comprises catalytically hydrogenating a glycosidic derivative of a pseudo-sapogenin acylated at least at the exo-hydroxyl group and in the sugar residues, with production of a glycosidic derivative of an exo-dihydro-pseudo-sapogenin acylated. at least at the exo-hydroxyl group and in the sugar residues, and mildly oxidizing said acylated glycosidic exo-dihydro-pseudo-sapogenin derivative in the sidechain attached to ring D, with production of an acylated glycosidic derivative of a steroid having in ring D the structure 3. The process for preparing steroidal compounds which comprises catalytically hydrogenating a glycosidic derivative of a pseud0-sapogenin acylated at least at the exo-hydroxyl group and in the sugar residues, with production of a glycosidic derivative of an exo-dihydro-pseudosapogenin acylated at least at the exo-hydroxyl group and in the sugar residues, mildly oxidizing said acylated glycosidic exo-dihydro-pseudosapogenin derivative in the side chain attached to ring D, with production of an acylated glycosidic derivative of a steroid having in ring D the structure and subjecting said acylated glycosidic derivative to hydrolysis with an acidic reagent, with production of a steroid having in ring D the structure and having, in the remainder of the steroid skeleton, hydroxyl groups in place of the sugar residues.

4. The process for the preparation of steroidal compounds which comprises isomerizing and acylating the side chain attached to ring D of a glycosidic derivative of the steroidal sapogenin by reacting said glycosidic derivative with an acylating agent under conditions more vigorous than those required for mere acylation, with production of a glycosidic derivative of a pseudosapogenin acylated at least at the exo-hydroxyl group and in the sugar residues, catalytically byand subjecting said acylated glycosidic derivative to hydrolysis with an acidic reagent, with' production of a steroid having in ring D the structure and having, in the remainder of the steroid skeleton, hydroxyl groups in place of the sugar residues.

RUSSELL EARL MARKER. HARRY MEANS CROOKS, JR. EUGENE LEROY .WITTLE. 

